PURPOSE: To reduce an amount of fuel stuck on a wall surface so as to prevent over-rich of an air-fuel ratio at the time of decelerating while obtaining good accelerating property by providing an opening control means for restricting the maximum opening of a throttle valve to a low level according to opening condition of an internal combustion engine.

CONSTITUTION: When an engine temperature is lowered more than a prescribed temperature, deterioration condition of fuel atomization is judged in an ECU 30 on the basis of a cooling water temperature, so that solenoid valves 27a, 27b are switch-operated. As a result, atmosphere pressure is led in the diaphragm chambers 26a, 26b of an actuator 26, and a control lever 22 is turned by a spring 23, so that the top end part 22a thereof is positioned to a position which is abutable on the step part 5b of a throttle lever 5. In this condition, when an acceleration pedal for accelerating is stepped in the maximum limit level, the step part 5b abuts on the top end part 22a of the control lever 22, and the turning amount of the throttle lever 5 is restricted, thereby intake flow speed and intake negative pressure become optimal in fuel atomization so as to obtain good acceleration property.